FIR: Unignore all blackbox tests on context receivers

compiler/testData/codegen/box/extensionFunctions/contextReceivers/overload.kt

@@ -1,7 +1,5 @@
 // !LANGUAGE: +ContextReceivers
 // TARGET_BACKEND: JVM_IR
-// IGNORE_BACKEND_FIR: JVM_IR
-// FIR status: context receivers aren't yet supported
 
 context(String, Int)
 fun overloaded(value: Any?) = "OK"
@@ -13,4 +11,4 @@ fun box() = with("42") {
     with(42) {
         overloaded(null)
     }
-}
+}